Carbon Dioxide CO2 Exposure Limits & Toxicity to humans:
This article series discusses normal and abnormal CO2 gas levels, the toxicity and exposure limits for exposure to carbon dioxide gas (CO2). We discuss Carbon Dioxide gas levels in outdoor air, in buildings, typical CO2 levels and conditions under which levels are unsafe.
We discuss the symptoms of carbon dioxide poisoning, describe different types of risks where high levels of CO2 may be present, and present data about the effects of CO2 exposure. Seek prompt advice from your doctor or health/safety experts if you have any reason to be concerned about exposure to toxic gases. Links on this page also direct the reader to carbon monoxide gas information in a separate document.
We give references and explanation regarding toxicity of Carbon Dioxide. Links on this page also direct the reader to carbon monoxide gas information in a separate document.
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IF YOU SUSPECT ANY BUILDING GAS-RELATED POISONING GO INTO FRESH AIR IMMEDIATELY and get others out of the building, then call your fire department or emergency services for help.
Symptoms of high or prolonged exposure to carbon dioxide include headache, increased heart rate, dizziness, fatigue, rapid breathing, visual and hearing dysfunctions. Exposure to higher levels may cause unconsciousness or death within minutes of exposure.
The photo (left) shows a Drager colorimetric gas detection tube used to test the CO2 levels in air. In an indoor air test (in our laboratory) the detector found that the CO2 level was about 600ppm which is typical of indoor air and is considered an acceptable and safe level.
While authorities indicate that CO2 is present in outdoor air at 0.035% , our own measurements [DF] indicate that at a given locality the actual CO2 level varies according to local conditions including temporal factors such as nearby fossil-fuel engines such as automobiles & buses.
In our measurements outdoors the typical carbon dioxide CO2 level in air typically varies between 300 ppm to 400 ppm. 400 ppm is a 0.04% concentration of a gas in air - slightly higher than the "official" figure.
When studying carbon dioxide levels inside of a building we therefore start with an outdoor baseline measurement, or several, obtained at varying distances from the structure. A comparison of the actual outdoor CO2 level with even a relatively low level of indoor CO2 (600 ppm and higher) may indicate a lack of adequate fresh air entering a building.
Carbon dioxide gas level measurements may be used in a study of indoor air quality even when the absolute levels of CO2 itself are not harmful. But as we explain below, at higher levels CO2 itself can affect building occupants and can even become dangerous or fatal.
What may be unclear in some cases is whether the sub-acute (sub-toxic) effects at modestly-elevated levels of CO2 in air stem from more from exposure to higher levels of carbon dioxide or whether they are due to reduced levels of oxygen. In an enclosed space such as a tight home or an enclosed basement or work space, increasing the level of CO2 is likely to simultaneously reduce the proportion of Oxygen (O2) in that same breathing air.
Some experts opine that complaints that seem to be associated with high CO2 problem in many if not most circumstances are likely to be actually due to the corresponding reduction in available oxygen in air rather than high toxicity levels of CO2 in the air. As carbon dioxide levels climb above a few percent the relative proportions of gases making up that air change: the concentration of oxygen in the air inhaled is reduced as the amount of CO2 is increased.
However, the TOXIC effects of elevated levels of CO2 are serious at levels when the oxygen reduction effects are only minor. 
IF YOU SUSPECT ANY BUILDING GAS-RELATED POISONING GO INTO FRESH AIR IMMEDIATELY and get others out of the building, then call your fire department or emergency services for help.
Here we discuss Carbon Dioxide gas levels in outdoor air, in buildings, typical CO2 levels and conditions under which levels are unsafe. We discuss the symptoms of carbon dioxide poisoning, describe different types of risks where high levels of CO2 may be present, and present data about the effects of CO2 exposure.
Seek prompt advice from your doctor or health/safety experts if you have any reason to be concerned about exposure to toxic gases. Links on this page also direct the reader to carbon monoxide gas information in a separate document.
- Daniel Friedman, with special thanks to Per Levéen, Telia Mobile, Sweden , Dr. Roy Jensen, (Canada) . and Stephen Fisher, B.Sc., Sales Director, K.D.Fisher & Company, Pty., Ltd., Australia,  for technical editing & comments.
Per Levéen has thoughtfully provided the detailed analysis comparing the hazards of elevated carbon dioxide in a building with the accompanying reduction of oxygen (O2 ) in the same space if the percentage of CO2 is increased from a leak from a CO2 gas cylinder.  The data following has been modified by Stephen Fisher, B.Sc, Dip. Ed., Sales Director of K.D.Fisher & Co., Pty. Ltd.
FACT: 100 liters of air contains:
Preliminary Assumptions: If the 100 litres is contained in a balloon like membrane, then 1.4 litres of gas can be added, at the same pressure. If we add 1.4 litres of CO2 to this mixture, we will get 101.4 litres of air which has an elevated CO2 content, and a reduced oxygen content, see the calculation immediately below:
Carbon Dioxide: (1.4 + 0.04) / 101.4 = 0.014 = 1.42 % CO2 by bolume in air
This is is an increase in CO2 percentage of 35.5 times above the “normal level” of 0.04% CO2 by volume in air. 1.42% CO2 can also be expressed as 14,000ppm (parts per million) CO2.
Oxygen: 20.9 / 101.4 = 0.206 = 20.6 % oxygen.
This is a reduction in the oxygen percentage of 0.3% by volume in air, below the “normal” 20.9% Oxygen by volume in air.
This change in the mix of gases in air when the level of CO2 increased results in a decrease with 1.4% in the oxygen level (and not 6.7% as was stated at Example of Reduced Oxygen Level in a Building)
However, KC Baczewski PE writes that the above calculation should be
((1.4/100)*20.9) = 0.29 %. i.e. a reduction in the “normal” oxygen level of 0.29%
You displace O2 and N2 for a final composition of:
Total = 100.00%.
Stephen Fisher agrees with this calculation method, which would involve extracting 1.4 litres of air, prior to the addition of the 1.4 litres of CO2 to the remaining 98.6 litres, which restores the total volume to 100 litres. This calculation has the advantage of providing a standard 100 litres of “air”, and consequently the number of litres of each component corresponds to the % by volume of each component gas of the mixture.
This is important because we recently had an accident with CO2 in Sweden killing two persons.
According to the newspapers CO2 is nontoxic and it is the decreased oxygen levels that kills. THIS CONCEPT IS WRONG.
Using the calculation equation above one can quickly conclude that adding 31 litres of CO2 to a 100 litre enclosed space would result in a 23.7% CO2 by volume in air, which would be almost instantly fatal, and 16% oxygen by volume in air, (equivalent to breathing at 2800 meters above sea level, which is dangerous, because it can lead to poor decision making, but not fatal).
It is the toxic properties of CO2 that is fatal, not the drop in oxygen.
In conclusion, in the event of a CO2 Cylinder leak, it is the toxic properties of CO2 that is fatal, long before oxygen levels have been reduced to fatally low levels.
According to the calculation shown below at Example of Reduced Oxygen Level in a Building, a level of 1.4% CO2 cause a drop of oxygen from 20.9% to 19.5%. As the arithmetic above shows, This calculation is misleading. Saying that adding 1.4% CO2 causes oxygen to drop to 20.9 - 1.4 = 19.5% is like saying that adding 20.9% CO2 would cause oxygen to drop to 20.9 - 20.9 = 0% That is of course not true. The correct and more precise calculation is provided above this paragraph.
Using either of the above calculation methods, the introduction of 5% CO2 to the room's air volume will reduce each of the components of normal air to 95% of their original proportion.
Standard Air Percentage
After Addition of 5% CO2
Carbon Dioxide (CO2)
A 5% level of CCO2 is directly toxic, yet as can be seen, the Oxygen level is at 19.85%, whereas the standard Australian 1st alarm level is set at 19.5%, so an oxygen sensor would not reach an alert level, despite serious CO2 levels being reached.
According to Example of Fatal levels of CO2 Carbon Dioxide in a Building (above), the math of the following example is not quite correct. We have kept Dr. Jensen's comments (below) but they should be read together with the detailed example and calculation provided above by Per Levéen.
More carbon dioxide may mean less oxygen: Let's say, sake of simplicity, that we're converting oxygen to carbon dioxide in an enclosed space. Then when the CO2 level has increased from its normal amount in air (about 0.03%) up to a higher concentration in air of 1.4% CO2 the concentration of oxygen in air will have decreased from 20.9 to 19.5%. Reducing the oxygen concentration from 20.9% down to 19.5% is equal to a 6.7% reduction in the oxygen level. -- Thanks to thanks to Dr. Roy Jensen for assistance with these details.
What are the effects on humans (and other animals) of reduction of the oxygen levels in air? At sea level, breathing air in which the O2 level has fallen to 16% percent is equivalent to being at the top of a 9,200-foot mountain - close to the level at which many people will experience shortness of breath while walking. 12% Oxygen in air at sea level corresponds to breathing normal air at an elevation of about 17,400 feet.
Original content, since extensively edited and expanded by several experts, began in 1985 with a literature search & search on Compuserve's Safety Forum by Dan Friedman. This is background information, obtained from expert sources. This text may assist readers in understanding these topics. However information presented here is not authoritative and may be incomplete.
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progression of high Carbon Dioxide in your body when it is 2% over the normal? / at what level do you do to STOP the the progression when it is 2% - E. Avery 7/23/2011
what is the distance i can plce the equipment in other to measure accurate reading of c02 emissions from a generator. - Afolabi 12/19/2011
I'm sorry but I can't quite see how to answer your question. A "generator" ??
The sensitivity and design-operating range of different types of gas detection equipment vary widely.
For example a ceiling mounted home carbon monoxide detector is intended to be placed at a variety of locations in a home, some many rooms away from the most likely CO source. But other test equipment may require distances ranging from centimeters to many meters. Our TIF 8800, for example, has a sensitivity adjustment. So without consulting the equipment instructions, there is no right answer to your question. And you scare us - let's hope no one's safety is relying on your approach.
This article is interesting. I think I understand the concept but I have an application that use an analyzer.
To calibrate this instrument, I need to use an 8% SO2 compress gas cylinder (cylinder capacity 5m3). This is located in a sealed 10x10x10 room, so my room is 1000m3 and unventilated.
Worst case scenario, the cylinder empties in this room. Is this an accute risk knowing that 3000 ppm is the LC50 (1/2hour) limit and the bottle contains 80000ppm? I have a bit of difficulties to put some math around this. Could you please explain?
I think 8% concentration x 5m3 cylinder = 0.4m3 of SO2 release in the room.
The gas will occupy 0.4m3/1000m3 = 0.04% of the room volume which is 400ppm.
400ppm < LC50 3000ppm = Low Risk?
- Syl 4/4/2-12
Syl, your question was a bit unclear and makes me worry that you are messing with gases without proper education or preparation. You are asking about Sulphur dioxide (SO2) in an article about Carbon dioxide (CO2) - in any event, if you are asking about recommended exposure limits for Sulphur dioxide SO2,
depending on the standard, SO2 PELs range among 0.25 ppm, 2 ppm, or 5 ppm.
please see details at
GAS EXPOSURE EFFECTS, TOXIC where below that title you'll see a link for Sulfur Dioxide Gas
those article links are at page top
Dan, I can assure you that nobody will be put in danger. Proper assessment will be done by qualified people for installation certification. Let me reformulate my question. I am interested to know how we determine if an area could be potentially dangerous or not. I mentioned SO2 but we can do it with CO2 if you like. The math behind is what I am looking for. Let's say for instance that a 5m3 gas cylinder containing 2000 ppm of CO2 is totally released in a 1000m3 closed room. What would be the indication of a gas detector located in the room, assuming the gas occupy the whole area due to an internal air movement (I understand that some area can have a higher concentration than other depending of the gas properties). I don’t think that a meter would read 1000ppm of CO2 because it is diluted in the air. What would be the reading in the middle of the room?
Why the health problems in space station reported by NASA long ago---at 500 ppm CO2 ? - Ron Schmoller 8/5/2012
Ron, if you can give us a citation, article, document source I'd be glad to take a look. A Google Scholar search for "Carbon dioxide hazards in the space station" didn't return a single article that addressed your question.
can a person whose had serious exposure to carbon monoxide still be experiencing some symptons such as memory lost and irrasionality 2-3 years after their exposure? - (Aug 11, 2012) firstname.lastname@example.org
Your question is posted on a carbon DIOXIDE page - please take a look at the Carbon MONOXIDE article (as that's what you're asking about) over at
CARBON MONOXIDE - CO (article links at page top)
for more details.
In general, your question is important enough that you should take it to your physician or to a physician who specializes in environmental medicine or gas exposure effects.
You don't define serious: serious to me could be a short term exposure to very high level of a gas, or a long term exposure to a lower level, perhaps even chronic exposure to a low level of a gas. The potential effects of gas exposure thus vary by type of exposure as well, of course, as by the gas itself and by individual susceptability.
With those general remarks, and the "serious" exposure not described, we can only engage in guessing and arm-waving.
Usually people recover fine from short term exposure to CO; chronic exposure, or prolonged exposure to a gas that basically is depriving a person of sufficient oxygen, could potentially cause more lasting problems. But if you are saying that the problems did not manifest themselves until two or three years later, I'd expect your doctor to be also considering some other, more immediate conditions.
Wonder if two people staying in a sedan car (sealed windows, no AC) will be suffocated of C02 in 30 minutes? - Atoi 9/10/2012
Atoi I think you are confusing CO (carbon monoxide) with CO2 (carbon dioxide) - or perhaps you are postulating that the automobile is airtight and that people are going to exhaust the available oxygen or suffer from high CO2 levels. In our experience, vehicles are not air tight, and the hazards arise from carbon monoxide from an idling engine or an exhaust leak, though I would agree that people breathing in an enclosed space will indeed push the CO2 numbers up.
Take a look at TYPICAL CO2 LEVELS - separate article for some examples of indoor or enclosed space carbon dioxide levels.
What is the mechanism of action in cases of carbon dioxide poisoning, assuming that the organism is provided adequate oxygen, that is, it does not suffocate? - H Durden 10/8/2012
The question you pose, along with both high CO2 effects and reduced oxygen efffects, is discussed in the article above.
5/18/2014 Anonymous said:
I have tried many times but fail to get a reply on how long it would take for the CO2 levels to get to dangerous levels in a closed sealed room. I am of course well aware that few rooms are really tightly sealed but in fact with better doors and window seatings this is becoming an iffy point and with security concerns my wife at least insists on closing the bedroom door. Surely some kind of measures can be given to a moderately intelligent person to guage likely extreme points.Also of course likely effects of worsening states can be given .. headaches ? etc.
(Aug 26, 2014) Anonymous said:
what is the standard management as work up and treatment approach
will you explain the approach consideration as regard the investigative tools for diagnosis and treatment protocol for CO2 poisoning cases
(Oct 8, 2014) joy said:
pls what are the mechanism toxic action of carbon oxide as an indoorpollutant
Anon, the problem may be the way you phrase the question.
There are clearly published exposure limits.
What's missing from the question as you put it is any data about concentrations. The concentration level of a ga in a space depends on a number of variables, such as (for an incomplete example)
Joy you'll want to take another look at the article above. Bascially, if high CO2 levels arise indoors the effect can be the replacement of oxygen. These articles, linked just above contain exposure limits & toxicity data
- the concentration of the gas that is entering the space
- the rate at which the gas is entering the space
- the rate at which fresh air is also entering or ventilating the space
- the volume of the space
These articles contain exposure limits & toxicity data
Please take a look at them and let me know if questions remain.
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